Many specialized terms and abbreviations are used in the communications arts. At least some of the following are referred to within the text that follows, such as in this background and/or the subsequent description sections. Thus, the following terms and abbreviations are herewith defined:
3GPP 3rd Generation Partnership Project
ACK Acknowledgment
ARQ Automatic Retransmission reQuest
CQI Channel Quality Indicator
DC-HSDPA Dual Carrier/Dual Cell HSDPA
DTX Discontinuous Transmission
HARQ Hybrid Automatic Retransmission reQuest
HSDPA High-Speed Downlink Packet Access
HS-DPCCH High-Speed Dedicated Physical Control Channel (in WCDMA)
HS-DSCH High-Speed Downlink Shared Channel
HSPA High Speed Packet Access
HS-SCCH High-Speed Shared Control Channel
MC-HSDPA Multiple Carrier/Multiple Cell HSDPA
MIMO Multiple Input, Multiple Output
NACK Negative Acknowledgment
POST ack/nack POSTamble
PRE ack/nack PREamble
WCDMA Wideband Code Division Multiple Access
Electronic communication forms the backbone of today's information-oriented society. Electronic communications are transmitted over wireless or wired channels using electromagnetic radiation, such as radio frequency (RF) transmissions, light waves, and so forth. The accessibility and capacity of electronic communications is frequently limited by the bandwidth of a communications channel between a first (e.g., transmitting) device and a second (e.g., receiving) device.
The available bandwidth of a communications channel may be increased by adopting any of a number of different schemes. One such example scheme is communicating over multiple carriers. Multiple carrier operations may include multiple cell operations. High speed packet access (HSPA), including high-speed downlink packet access (HSDPA), is currently being evolved to include multi-carrier and/or multi-cell operations. An initial step is to support dual-carrier and/or dual-cell (DC) HSDPA operations (DC-HSDPA). With DC-HSDPA, a user can receive from two carriers “simultaneously.” This increases high-data-rate coverage.
With some communication systems, such as those implemented in accordance with Wideband Code Division Multiple Access (WCDMA), communications between a sender and a receiver are performed with Automatic Retransmission reQuest (ARQ) or Hybrid ARQ (HARQ) operations. Thus, to support DC-HSDPA, an affirmative acknowledgement (ACK) or a negative acknowledgement (NACK) is used to support the HARQ operation on each of the two carriers. A number of proposals have been made to support the HARQ operations on each of two carriers.
A first proposal entails signaling the two ACK/NACK indications (one per carrier) using separate High-Speed Dedicated Physical Control Channels (HS-DPCCHs). However, it has been noted that such an approach has a severe coverage impact when both HS-DPCCHs are transmitted. Furthermore, when the second HS-DPCCH is transmitted alone, the cubic metric is slightly larger than when the first HS-DPCCH is transmitted alone. This results in worse coverage when a mobile needs to ACK/NACK the second carrier alone, as compared to when it needs to ACK/NACK the first carrier alone.
A second proposal generally entails signaling the two ACK/NACK indications using joint coding and one HS-DPCCH. In this approach, the two ACK/NACK messages are jointly encode and transmitted using one HS-DPCCH. There are eight (8) jointly-encoded messages to indicate the dual ACK/NACK conditions:
ACK (carrier 1) & ACK (carrier 2)
ACK (carrier 1) & NACK (carrier 2)
ACK (carrier 1) & DTX (carrier 2)
NACK (carrier 1) & ACK (carrier 2)
NACK (carrier 1) & NACK (carrier 2)
NACK (carrier 1) & DTX (carrier 2)
DTX (carrier 1) & ACK (carrier 2)
DTX (carrier 1) & NACK (carrier 2)
In the case of “DTX (carrier 1) and DTX (carrier 2)”, a mobile does not need to transmit any ACK/NACK signaling.
One specific proposal for joint encoding is to reuse the existing eight (8) MIMO ACK/NACK/PRE/POST code words that are specified in 3GPP TS 25.212 Table 15B. One example codebook in accordance with this specific proposal is given below:
ACK/DTX=[1 1 1 1 1 1 1 1 1 1]
NACK/DTX=[0 0 0 0 0 0 0 0 0 0]
DTX/ACK=[1 0 1 0 1 1 1 1 0 1]
DTX/NACK=[1 1 0 1 0 1 0 1 1 1]
ACK/ACK=[0 1 1 1 1 0 1 0 1 1]
ACK/NACK=[1 0 0 1 0 0 1 0 0 0]
NACK/ACK=[0 0 1 0 0 1 0 0 1 0]
NACK/NACK=[0 1 0 0 1 0 0 1 0 0].
Unfortunately, there are deficiencies in the existing proposals for supporting DC-HSDPA. As noted above, the former proposal with two separate ACK/NACK indications results in a severe coverage impact when both HS-DPCCHs are transmitted. The latter proposal results in a different set of deficiencies, which are described herein below.
Consequently, there is a need to address the deficiencies that exist in the current state of the art with regard to supporting multiple carrier and/or multiple cell communications (e.g., DC-HSDPA). Such deficiencies and other needs are addressed by one or more of the various embodiments of the present invention.